At least 3.5 billion years
Depends, what are the lengths given?
it might be c. this one is actually confusing. i am sorry that i couldn't help that much.
hope you get the answer you need.
~Hello there! ^_^
Your question: What country in East Asia is currently threatened by the expansion of its desert in its western regions...?
Your answer: Taiwan is the East Asian country that is currently threatened by the expansion of its desert in its western regions.
The answer is option C.
Hope this helps! :D